Transmeta Rewrites the Rules

Processor designers and software designers typically work for
different companies. If they do work at the same company, they
rarely deign to speak to one another. At Transmeta, these engineers
work hand in hand. The unique combination of hardware and
code-morphing software allows them to solve problems in ways no
other company can.

This is because the CMS is the only code that uses Crusoe's
VLIW instructions; all other software for the chip is written in
x86 code. Therefore, the processor designers are freed from the
burden of maintaining compatibility; in fact, the first two
Transmeta chips are not even compatible with each other! Each uses
its own version of the CMS, and both are fully compatible with all
x86 programs through code morphing. If the hardware team wants to
give the chip a feature that improves performance or reduces cost,
they need only clear it with their compatriots in CMS land, and the
change can be made. Conversely, a bug in the hardware design can
often be solved by telling the CMS “don't do that”, avoiding a
costly and time-consuming redesign of the chip.

The biggest fear of an Intel CPU engineer is that their
design will have a bug that prevents some application from running
correctly. The infamous Pentium floating-point bug cost the company
hundreds of millions of dollars in 1995. In contrast, if the CMS
doesn't execute an x86 application correctly, the CMS can usually
be patched and reissued within a matter of days. Crusoe may be the
first microprocessor to be upgraded in the field. CMS engineers
also ask for and receive hardware changes that accelerate x86
execution. Previous attempts to implement x86 compatibility in
software, such as Sun's WABI (x86 on SPARC) and Digital's FX!32
(x86 on Alpha), failed because they didn't offer the right
combination of 100% compatibility and competitive performance.
Neither SPARC nor Alpha offers any support for x86 in hardware,
whereas the Crusoe chips include small but important circuits that
speed the code-morphing software beyond what previous efforts
achieved.

Competing in Mobile PCs

With its low power and x86 compatibility, Crusoe is an
obvious fit for a notebook PC. The processor runs Microsoft Windows
and standard PC software, just like a system that uses an Intel or
AMD processor. Its low power extends battery life and reduces the
amount of heat the processor gives off. With a cooler chip,
notebook makers can take out fans and heat sinks that add weight,
burn power and make noise. Not satisfied with the inherent benefits
of its VLIW design, Transmeta developed its LongRun technology to
further trim Crusoe's power consumption. During operation, the CMS
monitors the workload of the processor and dynamically adjusts its
clock speed to match. Unlike other chips, Crusoe can reduce its
voltage as well as its clock speed; because CMOS power equals
cv<+>2<+>f, at 50% workload the chip needs less than
20% of its peak power.

LongRun was announced the day after Intel's SpeedStep
technology, which also changes clock speed and voltage in mobile
systems. SpeedStep processors go faster when the notebook PC is
plugged into the wall, but SpeedStep has no effect in battery mode.
In contrast, LongRun conserves power, extending battery life when a
notebook user is on the go. The low power of Crusoe will extend the
battery life of traditional notebook PCs, but only by 30% or so in
most situations. That's because the CPU typically consumes about a
quarter of the battery's output, with most of the rest used by the
display backlight, hard drive and CD-ROM drive. Transmeta likes to
focus on applications, such as DVD, that are more CPU-intensive and
therefore have a bigger advantage on Crusoe. But simply adding
Crusoe to today's notebook PCs will not result in an eight-hour
battery life.

Creating a New Class of Devices

Crusoe's power advantage is more critical in the emerging
market for portable web devices. In a wireless web pad with no
drives (see Figure 3), the CPU is a large part of the power budget.
Intel suggests its Celeron processor for these devices, but Celeron
burns too much power for extended battery life. Intel's StrongArm
chip uses even less power than Crusoe, but doesn't offer x86
compatibility.

Figure 3. Prototype Web Pad Using Crusoe Chip

Why is x86 compatibility important? After all, these devices
don't run Windows or Windows software; they use an embedded
operating system, in some cases the new Mobile Linux, and a browser
that has been compiled specifically for the internal
processor.

Transmeta points out that many browser plug-ins are written
in x86 code. To get the full web experience, a web pad must be able
to download and execute new plug-ins. Without these plug-ins, some
web pages simply won't work. To offer the same experience for a
StrongArm web pad, a system vendor would have to fund the porting
of each new plug-in to the StrongArm instruction set.

Instead, Crusoe offers out-of-the-box compatibility with all
web content. In addition, it gives the system maker the choice of
Linux, Windows CE, or any other operating system that already runs
on the x86 platform. Crusoe also supports all of the popular x86
software-development tools. The chip's low power and x86
compatibility give it a clear advantage in this market
segment.

The bad news is that the market for web pads is basically
nonexistent, limiting Transmeta's potential sales. Crusoe burns too
much power for today's most popular portable web device, the Palm
VII. But this market could grow to tens of millions of units over
the next five years, and Transmeta is poised to grow along with
it.

By boldly combining hardware and software in a new way,
Transmeta has built a processor with clear advantages in power and
compatibility. If Transmeta delivers on its performance claims,
Crusoe should launch a new class of devices which let you take the
Web wherever you go. With their code-morphing software, Crusoe
devices will run nearly any operating system. But as Transmeta's
Torvalds says with a smile, they will run Linux just a little bit
better.

Linley Gwennap
(linley@linleygroup.com)
is the founder and principal analyst of The Linley Group
(http://www.linleygroup.com/),
a technology analysis firm in Mt. View, California. He is a former
editor in chief of Microprocessor Report.